The forestry industry is responsible for large-scale propagation and development of coniferous trees. This involves the careful nurturing of seeds or tree embryos to seedlings under controlled greenhouse conditions. Typically, the seedlings are grown in trays comprising a plurality of soil plugs generally arranged in ordered rows. Each soil plug comprises the root system of an individual seedling, the ‘above-ground’ portion of the seedling, including the needles, extending from the soil plug. The presence of a polymeric binding substance, which is optionally mixed with the plant growing media, can help to preserve the integrity of the soil plug during seedling transportation or transplantation.
Soil plugs generally have limited sizes and can only sustain continued seedling development for a limited period. Once a seedling has grown to a predetermined size (dependent upon the size of the soil plug) the seedling must be transplanted either to a larger soil plug or into the ground. In the forestry industry, it is often impractical to transfer seedlings to successively larger soil plugs. Therefore, the seedlings are typically transferred directly into the ground, once they have attained a viable size and root system.
A number of machines are known in the art for the automated transplantation of seedlings. However, the inventors are aware of significant inadequacies in the use of such prior art machines for the transplanting of coniferous tree seedlings for the forestry industry.
In one example of the prior art, U.S. Pat. No. 4,660,479, issued Apr. 28, 1987, discloses a trailer-type apparatus for planting canisters contained seedlings. The apparatus includes a furrow forming plow followed by a backfill blade sequentially operated for forming the furrow and covering the roots of a seedling deposited in the furrow. The apparatus also includes a belt-type conveyor provided with transverse recesses, which receives canister contained tree seedlings from a supply hopper and deposits the seedlings in sequence on a seedling supporting ramp. A pressure cylinder plunger separates the seedling from its canister and deposits it on a pivoting platform lowering the seedling by gravity into a sleeve chute where it is temporarily supported until a quantity of water, released from an adjacent tank, washes the seedlings out of a chute to fall into an underlying furrow.
In another example, U.S. Pat. No. 4,765,260, issued Aug. 23, 1988, discloses a machine for transplanting seedlings, which comprises a chassis onto which are connected a plurality of planting units. Each unit comprises a double pathway defined by a double end-less chain which carries sleeve shaped members, and an air stream assisted seedling supply means respectively engagable with each sleeve member for supplying a seedling into each sleeve when each sleeve is inserted into the ground. The machine further comprises a rotating member which carries pointed dibbles that become inserted through each sleeve member moving on a pathway with the endless chain into the soil, for making a hole in the ground to assist insertion of the seedling.
In a final example, U.S. Pat. No. 4,355,588, issued Oct. 26, 1982, discloses a machine for transplanting soil plugs comprising a conveyor having a plurality of soil plug gripping mechanisms mounted thereto, a furrow opening device, and a furrow closing device. Generally, the furrow closing device is defined by portions of a bed shaper that operates to form the soil into a trapezoidal planting bed. In addition, the bed shaper establishes a ground level with respect to which the plugs are planted, in which the rear portions of the bed shaper act to close the furrow. Each plug gripping assembly preferably comprises a centre opening clip having opposed resilient fingers. The conveyor path is characterized by a lower horizontal path portion that maintains the plugs at the proper planting depth for a significant interval so that the soil may be properly closed around the plugs before the plugs are released.
The rapid, automated handling of soil plugs, and the plants grown therein, has presented significant challenges to the forestry industry. As discussed, a number of automated transplanters are known in the art, which extract soil plugs from trays, and transfer the soil plugs to a planting position adjacent the ground. However, many such machines are generally adapted for handling agricultural crops, rather than coniferous tree seedlings.
The inventors of the present invention have found that the machines of the prior art are not ideally suited to the handling of tree seedlings. Compared to most agricultural crops, tree seedlings are relatively fragile and must be handled with great care to avoid damage. To remain viable, tree seedlings require accurate placement in the ground at a predetermined depth and orientation. Misplacement of tree seedlings, for example at an improper depth, or a non-vertical orientation, can result seedling loss.
In contrast to many agricultural crops, it is often desirable to plant tree seedlings under soil conditions that are less than ideal for automated planting. For example, such soil conditions may include undulating or uneven soil, hard-baked soil, or water-saturated soil. The automated transplanters of the prior art generally operate only at optimum soil conditions, and provide less than satisfactory results under adverse soil conditions. For example, some transplanters even require laser-levelled fields in order to ensure accurate placement and planting of seedlings. Therefore, there is a continuing need to develop machinery and corresponding systems that ensure accurate planting of seedlings, including tree seedlings, to an accurate planting depth under less than optimum soil conditions.
Furthermore, there is a continuing need to develop transplanting machines that enable tree seedlings to be planted rapidly, and in a high density, for example, a density of up to 24 seedlings per square foot. This density would permit efficient land usage and facile seedling maintenance, and also confer a degree of resistance to adverse environmental factors such as wind damage.